Time Trade-off Research Articles

PCR96 Effects of Intravenous Iron Infusion Frequency, Duration, and Safety on Quality of Life: Results of a Time Trade-Off Study in Patients With Iron Deficiency Anemia in China

Intravenous (IV) iron is the preferred and most efficacious treatment for patients with iron deficiency anemia (IDA) when oral iron cannot be used or where rapid iron delivery is required; however, IV infusions are invasive and e.g. require patients to be hospitalized or travel to specialist infusion units, which can have a detrimental effect on quality of life. The required number and duration of infusions varies between IV iron formulations. The aim of the present study was to elicit health state utility values (HSUVs) from a population of IDA-patients in China and to compare the results with a previous study conducted in the general population.

SA81 Feasibility and Challenges of Virtual Time Trade-Off Interviews: The Case of the EQ-5D-3L Valuation Study in Jordan

SA81 Feasibility and Challenges of Virtual Time Trade-Off Interviews: The Case of the EQ-5D-3L Valuation Study in Jordan

PCR43 Comparison of Face-to-Face and Online Surveys of Measuring Utility for Metastatic Pancreatic Cancer in Japan Using Composite Time Trade-Off

PCR43 Comparison of Face-to-Face and Online Surveys of Measuring Utility for Metastatic Pancreatic Cancer in Japan Using Composite Time Trade-Off

PCR125 Censoring in the Time Trade-Off Valuation of Worse-Than-Dead EQ-5D-5L Health States: Can a Willingness-to-Accept Question be the Solution?

PCR125 Censoring in the Time Trade-Off Valuation of Worse-Than-Dead EQ-5D-5L Health States: Can a Willingness-to-Accept Question be the Solution?

The Egyptian EQ-5D-5L Extensive Pilot Study: Lessons Learned.

To investigate the effect of an extensive pilot phase in improving protocol compliance, face validity, reduction of interviewer effect and prediction errors in the composite time trade-off (cTTO) data elicited as part of the EQ-5D-5L valuation study in Egypt. This study used the cTTO data and quality control (QC) reports from the Egyptian EQ-5D-5L valuation study. Three-level mixed models were estimated to test whether interviewer effects were reduced during the pilot phase and subsequent rounds of collected cTTO data. Ordinary least square (OLS) regression analysis was conducted for each interviewer separately to test whether the mean absolute error (MAE) improved as interviewers completed more interviews. Moreover, improvement in protocol compliance, face validity and reduction of prediction errors in the cTTO data were tested. 1180 interviews were conducted by nine interviewers and included in the final analysis, of which 206 interviews were pilot and 974 interviews were actual. There was substantial improvement in the face validity and reduction of prediction errors in the cTTO data where the MAE of the actual data was 0.37, which is much lower than that of the pilot data, which was 0.44. However, there was an initial high level of protocol compliance in terms of the four indicators of the QC tool and the variance attributed to the interviewers was small throughout the whole study. This study clarified the benefits of the pilot phase and the strict implementation of the QC tool in improving the face validity and the prediction accuracy of the cTTO data. However, a more extensive pilot phase may be more beneficial in EQ-5D-5L valuation studies that have issues initially with protocol compliance and interviewer effects.

Preference-based comparison of quality of life associated with vision loss in Black and White ophthalmic populations in the US

ObjectifLe concept d'utilité consiste en une estimation des préférences individuelles, dont la fourchette s’étend normalement de 1,00 (meilleur état de santé possible) à 0,00 (décès). L'utilité permet de mesurer l'amélioration de la qualité de vie en lien avec une intervention de soins de santé. Conjointement à l'augmentation de l'espérance de vie, elle permet – selon le type d'intervention – d’évaluer le gain total de valeur lié à l'intervention en années de vie ajustées en fonction de la qualité, lequel peut être intégré aux coûts dans le cadre d'une analyse coût-utilité. À notre avis, il était pertinent de vérifier si la race représentait un facteur de confusion de l'utilité en ce qui a trait à la vision. MéthodesOn a réalisé une analyse des données transversales des dossiers de patients noirs et caucasiens ambulatoires consécutifs qui ont consulté les cabinets d'ophtalmologie du Wills Eye Hospital (Philadelphie, Pennsylvanie), cabinets prenant part à une étude de longue durée (1999 à 2016) évaluant l'utilité relative à la vision au moyen de la technique de l'arbitrage temporel (ou TTO, time trade-off). Chaque participant a été interviewé par un chercheur grâce à un outil d'arbitrage temporel validé et fiable de mesure de l'utilité relative à la vision, puis une cote de 1 à 5 était attribuée à la vision en fonction de l'acuité visuelle du meilleur œil. Les résultats de l'analyse d'utilité ont été comparés à l'aide d'un test t bilatéral et du test U de Mann-Whitney. RésultatsAinsi, 1125 patients consécutifs qui étaient en mesure de répondre aux questions ont été inclus à notre étude. En présence d'une vision 20/200–20/800, les résultats moyens de l'analyse d'utilité relative à la vision des patients caucasiens/noirs s’élevaient respectivement à 0,58/0,59 (p = 0,84); en présence d'une vision 20/70–20/100, les résultats s’élevaient respectivement à 0,72/0,70 (p = 0,85); en présence d'une vision 20/50–20/60, les résultats s’élevaient respectivement à 0,78/0,79 (p = 0,86); en présence d'une vision 20/25–20/50, les résultats s’élevaient respectivement à 0,84/0,88 (p = 0,16) et, enfin, en présence d'une vision 20/20, les résultats s’élevaient respectivement à 0,91/0,90 (p = 0,43). ConclusionsL'analyse de l'utilité relative à la vision par arbitrage temporel chez des patients noirs et caucasiens qui consultent un cabinet d'ophtalmologie a donné des résultats semblables, et ce, aux différents degrés d'acuité visuelle. On peut donc conclure à une qualité de vie similaire, de sorte que les valeurs d'utilité relatives à la vision acquises par arbitrage temporel qui sont utilisées dans les analyses coût-utilité n'ont pas besoin d’être ajustées en fonction de la race (noire ou caucasienne) des patients qui reçoivent des soins ophtalmologiques aux États-Unis.

138 Comparative analysis of patient’s direct indirect and dermatology specific utility values in four dermatological diseases

We aim compare time trade-off (TTO), EQ-5D-5L and Dermatology Life Quality Index (DLQI) utility measures based on patients’ preferences in atopic dermatitis, hidradenitis suppurativa, pemphigus & psoriasis. Secondary objective is to determine the effect of sociodemographic characteristics that impact utility scores. Four multi-centre cross sectional surveys were carried out between 2014-2022 in Hungary, using paper-based self administrated data collection method. Conventional TTO task with 10 year timeframe was applied to elicit direct health utility.

Analytical Considerations When Anchoring Discrete Choice Experiment Values Using Composite Time Trade-Off Data: The Case of EQ-5D-Y-3L.

Discrete choice experiments (DCEs) are becoming increasingly used to elicit preferences for children's health states. However, DCE data need to be anchored to produce value sets, and composite time trade-off (cTTO) data are typically used in the context of EQ-5D-Y-3L valuation. The objective of this paper is to compare different anchoring methods, summarise the characteristics of the value sets they produce, and outline key considerations for analysts. Three anchoring methods were compared using data from published studies: (1) rescaling using the mean value for the worst health state; (2) linear mapping; and (3) hybrid modelling. The worst state rescaling value set had the largest range. The worst state rescaling and linear mapping value sets preserved the relative importance of the dimensions from the DCE, whereas the hybrid model value set did not. Overall, the predicted values from the hybrid model value set were more closely aligned with the cTTO values. These findings are relatively generalisable. Deciding upon which anchoring approach to use is challenging, as there are numerous considerations. Where cTTO data are collected for more than one health state, anchoring on the worst health state will arguably be suboptimal. However, the final choice of approach may require value judgements to be made. Researchers should seek input from relevant stakeholders when commencing valuation studies to help guide decisions and should clearly set out their rationale for their preferred anchoring approach in study outputs.

Patient preferences for treatment modalities for localised prostate cancer.

To assess the patient preferences and utility scores for the different conventional and innovative treatment modalities for localised prostate cancer (PCa). Patients treated for localised PCa and healthy volunteers were invited to fill out a treatment-outcome scenario questionnaire. Participants ranked six different treatments for localised PCa from most to least favourable, prior to information. In a next step, treatment procedures, toxicity, risk of biochemical recurrence and follow-up regimen were comprehensibly described for each of the six treatments (i.e. treatment-outcome scenarios), after which patients re-ranked the six treatments. Additionally, participants gave a visual analogue scale (VAS) and time trade-off (TTO) score for each scenario. Differences between utility scores were tested by Friedman tests with post hoc Wilcoxon signed-rank tests. Eighty patients and twenty-nine healthy volunteers were included in the study. Before receiving treatment-outcome scenario information, participants ranked magnetic resonance-guided adaptive radiotherapy most often as their first choice (35%). After treatment information was received, active surveillance was most often ranked as the first choice (41%). Utility scores were significantly different between the six treatment-outcome scenarios, and active surveillance, non- and minimal-invasive treatments received higher scores. Active surveillance and non-invasive treatment for localised PCa were the most preferred options by PCa patients and healthy volunteers and received among the highest utility scores. Treatment preferences change after treatment information is received.

Censoring Time Trade-off Values at 0 Versus at −1: How Does the Assumption for Worse-Than-Dead Time Trade-off Values Affect the Modeling of EQ-5D-5L Valuation Data?

ObjectivesA recent study found that negative utility values elicited using composite time trade-off (TTO) were barely associated with the severity of EQ-5D-5L health states, suggesting poor discriminative ability. Assuming negative values provide limited information, this study aimed to explore the usefulness of censoring negative TTO values at 0 in modeling EQ-5D-5L valuation data. MethodsWe analyzed EQ-5D-5L valuation data from China, The Netherlands, Canada, Singapore, and Thailand. For each data set, we estimated value sets using 2 Tobit models, one left-censored at −1 (current practice) and one left-censored at 0 (our proposed method), and compared the model performances. We hypothesized that censoring at 0 and censoring at −1 would produce similar values, though on slightly different scales. ResultsWhen censoring at 0, logical inconsistencies and statistical significance were improved but the value range was compressed. In the cross-attribute level effects model, the 3-level parameters were similar between the models censored at 0 and −1, but the rank order of some dimension parameters was altered. Health state values predicted by the 2 censoring models approximated a perfect agreement after rescaling. ConclusionsCensoring TTO values at 0 improved model estimation and fit but produced higher utility values than models censoring at −1. Investigators of future EQ-5D value set studies using the composite TTO method are advised to examine the validity of negative TTO values before choosing modeling strategies.

Estimating an EQ-5D-Y-3L Value Set for Indonesia by Mapping the DCE onto TTO Values.

Methods for estimating health values in adult populations are well developed, but lag behind in children. The EuroQol standard protocol to arrive at value sets for the youth version of the EQ-5D-Y-3L combines discrete choice experiments with ten composite time trade-off values. Whether ten composite time trade-off values are sufficient remains to be seen and this is one of the reasons the protocol allows for experimental expansion. In this study, 23 health states were administered for the composite time trade-off. This methodological research is embedded in a study aimed at generating a representative value set for EQ-5D-Y-3L in Indonesia. A representative sample of 1072 Indonesian adults each completed 15 discrete choice experiment choice pairs via face-to-face interviews. The discrete choice experiment responses were analysed using a mixed-logit model. To anchor the discrete choice experiment values onto the full health-dead quality-adjusted life-year scale, composite time trade-off values were separately obtained from 222 adults living in Java for 23 EQ-5D-Y-3L states. The derived latent discrete choice experiment values were mapped onto the mean observed composite time trade-off values to create a value set for the EQ-5D-Y-3L. Linear and non-linear mapping models were explored to estimate the most efficient and valid model for the value set. Coefficients obtained from the choice model were consistent with the monotonic structure of the EQ-5D-Y-3L instrument. The composite time trade-off data showed non-linearity, as the values for the two worst states being evaluated were much lower than predicted by a standard linear model estimated over all composite time trade-off data. Thus, the non-linear mapping strategies with a power term outperformed the linear mapping in terms of mean absolute error. The final model gave a value range from 1.000 for full health (11111) to -0.086 for the worst health state (33333). Values were most affected by pain/discomfort and least by self-care. This article presents the first EQ-5D-Y-3L value set for Indonesia based on the stated preferences of adults asked to consider their views about a 10-year-old child. Mapping the mixed-logit discrete choice experiment model with the inclusion of a power term (without a constant) allowed us to generate a consistent value set for Indonesian youth. Our findings support the expansion of the composite time trade-off part of the EQ-5D-Y valuation study design and show that it would be wise to account for possible non-linearities in updates of the design.

The impact of skin disfigurement in patients with autoimmune connective tissue disorders on quality of life, willingness-to-pay, and time trade-off: A cross-sectional analysis

The impact of skin disfigurement in patients with autoimmune connective tissue disorders on quality of life, willingness-to-pay, and time trade-off: A cross-sectional analysis

An EQ-5D-Y-3L Value Set for Belgium.

In Belgium, a value set for children and adolescents for a generic health-related quality-of-life measure is not available. To inform drug pricing and make resource allocation decisions for children and adolescents, national tax-payers' preferences for youth health states should be known. We aimed to obtain a value set for EQ-5D-Y-3L in Belgium, following the international youth valuation protocol for data collection. Composite Time Trade-Off interviews were conducted in a sample of 200 adults, either face to face or via video conferencing. Another sample of 1000 adults completed an online discrete choice experiment survey. All adults were asked to take the perspective of a 10-year-old child for both methods. Both samples were representative for Belgium in terms of age, sex and region. A latent class analysis was selected to obtain the relative importance of the five dimensions and their levels based on the discrete choice experiment data, which were anchored with the composite Time Trade-Off censored value for the worst health state (33333). Preferences from Belgian adults revealed a mean censored value for 33333 for children and adolescents of -0.475. All the estimated coefficients of the modelwith 4 latent classes were statistically significant and showed higher disutility as severity levels increase. The most important health dimension was pain/discomfort, followed by feeling sad/worried/unhappy. This study presents the Belgian EQ-5D-Y-3L value set, which will be included in the Belgian pharmacoeconomic guidelines. The value set enables the calculation of quality-adjusted life-years in children and adolescents, allowing a cost-effectiveness evaluation of health technologies and their youth-specific price setting.

Do they just know more, or do they also have different preferences? An exploratory analysis of the effects of self-reporting serious health problems on health state valuation

BackgroundHealth state valuation is often conducted by people valuing either only their own health state (experience-based valuation) or several stylised states (hypothetical valuation). The approach used can affect the elicited values, but it is not clear whether this is caused by different understandings of the states (an “information mechanism”) and/or by different opinions of the states (a “preference mechanism”). Justifying privileging the valuations of those with the relevant health state experience solely because they are better informed is insufficient when their opinions differ. This study proposes a new framework to examine the effect of having health problems on health state valuation by distinguishing “within-dimensional” effects (which can be due to better information or due to differences in opinion) and “cross-dimensional” effects (which must be due to differences in opinion). MethodsSecondary data from the UK that valued EQ-5D-5L using Discrete Choice Experiments with duration (DCETTO) are remodelled controlling for whether a respondent self-reports serious (viz., severe or extreme) problems in “pain or discomfort” (PD) or “anxiety or depression” (AD). The main analysis uses respondents who have serious PD or serious AD alongside matched respondents who do not, and assumes constant proportional time trade-off. ResultsSelf-reporting serious PD or serious AD problems has no within-dimensional effect on health state preferences. However, self-reporting serious AD problems has negative cross-dimensional effects on the utility of having any problem in PD, which suggests that the preference mechanism is present. A similar pattern holds when all available (unmatched) data are used and when constant proportional time trade-off is relaxed. ConclusionsFindings consistent with the preference mechanism indicate that those with serious health problems may have different opinions on the value of health states compared to the rest of the population, which has normative implications for the debate on which values to use.

In a Child's Shoes: Composite Time Trade-Off Valuations for EQ-5D-Y-3L with Different Proxy Perspectives.

Background and ObjectivesEQ-5D-Y-3L health states are commonly valued by asking adults to complete stated preference tasks, ‘given their views about a 10-year-old child’ (hereafter referred to as proxy 1). The use of this perspective has been a source of debate. In this paper, we investigated an alternative proxy perspective: i.e. adults considered what they think a 10-year old-child would decide for itself (hereafter, proxy 2 (substitute)]. Our main objective was to explore how the outcomes, dispersion and response patterns of a composite time trade-off valuation differ between proxy 1 and proxy 2.MethodsA team of four trained interviewers completed 402 composite time trade-off interviews following the EQ-5D-Y-3L protocol. Respondents were randomly allocated to value health states in either the proxy 1 or proxy 2 (substitute) perspective. Each respondent valued ten health states with the perspective they were assigned to, as well as one health state with the alternative perspective (33333).ResultsThe use of different proxy perspectives yielded differences in EQ-5D-Y-3L valuation. For states in which children had considerable pain and were very worried, sad or unhappy, respondents’ valuations were lower in proxy 1 than in proxy 2 (substitute) perspectives, by about 0.2. Within-subject variation across health states was lower for proxy 2 (substitute) than proxy 1 perspectives. Analyses of response patterns suggest that data for proxy 2 (substitute) perspectives were less clustered.ConclusionsThere are systematic differences between composite time trade-off responses given by adults deciding for children and adults considering what children would want for themselves. In addition to warranting further qualitative exploration, such differences contribute to the ongoing normative discussion surrounding the source and perspective used for valuation of child and adolescent health.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40273-022-01202-1.

Modifying the Composite Time Trade-Off Method to Improve Its Discriminatory Power

ObjectivesIn cost-effectiveness analysis of health technologies, health state utilities are needed. They are often elicited with a composite time trade-off (cTTO) method, particularly for the widely used EQ-5D-5L. Unfortunately, cTTO discriminatory power is hindered by (1) respondents’ nontrading (NT) of time for quality, (2) censoring of utilities at −1, and (3) poor correlation of negative utilities with state severity. We investigated whether modifying cTTO can mitigate these effects. MethodsWe interviewed online 478 students (February to April, 2021) who each valued the same 10 EQ-5D-5L health states in 1 of 3 arms. Arm A used a standard cTTO, expanded with 2 questions to explore reasons for NT and censoring. Arms B and C used a time trade-off with modified alternatives offered to overcome loss aversion, to unify the tasks for positive and negative utilities, and to enable eliciting utilities < −1. ResultsIn arms B and C, we observed less NT than in A (respectively, 4% and 4% vs 10%), more strictly negative utilities (38% and 40% vs 25%), and more utilities ≤ −1 (18% and 30% vs 10%). The average utility of state 55555 dropped to −2.15 and −2.52 from −0.53. Enabling finer trades in arm A reduced NT by 70%. Arms B and C yielded an intuitive association between negative utilities and state severity. These arms were considered more difficult and resulted in more inconsistencies. ConclusionsThe discriminatory power of cTTO can be improved, but it may require increasing the difficulty of the task. The standard cTTO may overestimate the utilities, especially of severe states.

A Value Set for the EQ-5D-Y-3L in the Netherlands.

Background and ObjectiveThere is increasing interest in preference-accompanied measures of health for paediatric populations. The child-friendly EQ-5D version, EQ-5D-Y-3L, is one such instrument, but the lack of a Dutch value set prevents its use in economic evaluations of healthcare interventions in the Netherlands. This study aims at covering this gap by collecting preferences using a standardised protocol for deriving EQ-5D-Y-3L value sets.MethodsComposite time trade-off data were collected using videoconferencing interviews, with each respondent completing ten composite time trade-off tasks. Discrete choice experiment data were collected using an online survey, with respondents each completing 15 paired comparisons. Respondents completed these tasks considering what they prefer for a hypothetical 10-year-old child. Discrete choice experiment data were analysed using a ten-parameter mixed-logit model and anchored to the quality-adjusted life-year scale using the mean observed composite time trade-off values.ResultsThe study collected preferences for 197 respondents using composite time trade-off and for 959 respondents using a discrete choice experiment. The discrete choice experiment sample was representative for the Dutch population in terms of age and sex. The level 3 weight for pain/discomfort was the largest, followed by feeling worried, sad or unhappy, usual activities, mobility and self-care. Health state values ranged between −0.218 and 1.ConclusionsThis study generated a Dutch value set for the EQ-5D-Y-3L, which can be used for the computation of quality-adjusted life-years for economic evaluations of healthcare interventions in paediatric populations.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40273-022-01192-0.

Cost-Effectiveness of a Specialized Breathlessness Service Versus Usual Care for Patients With Advanced Diseases

ObjectivesThe Munich Breathlessness Service (MBS) significantly improved control of breathlessness measured by the Chronic Respiratory Questionnaire (CRQ) Mastery in a randomized controlled fast track trial with waitlist group design spanning 8 weeks in Germany. This study aimed to assess the within-trial cost-effectiveness of MBS from a societal perspective. MethodsData included generic (5-level version of EQ-5D) health-related quality of life and disease-specific CRQ Mastery. Quality-adjusted life years (QALYs) were calculated based on 5-level version of EQ-5D utilities valued with German time trade-off. Direct medical costs and productivity loss were calculated based on standardized unit costs. Incremental cost-effectiveness ratios (ICER) and cost-effectiveness–acceptance curves were calculated using adjusted mean differences (AMD) in costs (gamma-distributed model) and both effect parameters (Gaussian-distributed model) and performing 1000 simultaneous bootstrap replications. Potential gender differences were investigated in stratified analyses. ResultsBetween March 2014 and April 2019, 183 eligible patients were enrolled. MBS intervention demonstrated significantly better effects regarding generic (AMD of QALY gains of 0.004, 95% confidence interval [CI] 0.0003 to 0.008) and disease-specific health-related quality of life at nonsignificantly higher costs (AMD of €605 [95% CI −1109 to 2550]). At the end of the intervention, the ICER was €152 433/QALY (95% CI −453 545 to 1 625 903) and €1548/CRQ Mastery point (95% CI −3093 to 10 168). Intervention costs were on average €357 (SD = 132). Gender-specific analyses displayed dominance for MBS in males and higher effects coupled with significantly higher costs in females. ConclusionsOur results show a high ICER for MBS. Considering dominance for MBS in males, implementing MBS on approval within the German health care system should be considered.

Value Set for the EQ-5D-Y-3L in Hungary.

BackgroundThe Hungarian health technology assessment guidelines recommend the use of the EuroQol instrument family in quality-adjusted life-year calculations. However, no national value set exists for the EQ-5D-Y-3L or any other youth-specific instrument.ObjectiveThis study aims to develop a national value set of the EQ-5D-Y-3L for Hungary based on preferences of the general adult population.MethodsThis study followed the international valuation protocol for the EQ-5D-Y-3L. Two independent samples, representative of the Hungarian general adult population in terms of age and sex were recruited to complete online discrete choice experiment (DCE) tasks and composite time trade-off (cTTO) tasks by computer-assisted personal interviews. Adults valued hypothetical EQ-5D-Y-3L health states considering the health of a 10-year-old child. DCE data were modelled using a mixed logit model with random-correlated coefficients. Latent DCE utility estimates were mapped onto mean observed cTTO utilities using ordinary least squares regression.ResultsOverall, 996 and 200 respondents completed the DCE and cTTO surveys, respectively. For each domain, the value set resulted in larger utility decrements with more severe response levels. The relative importance of domains by level 3 coefficients was as follows: having pain or discomfort > feeling worried, sad or unhappy > mobility > doing usual activities > looking after myself. Overall, 12.3% of all health states had negative utilities in the value set, with the worst health state having the lowest predicted utility of − 0.485.ConclusionThis study developed a national value set of the EQ-5D-Y-3L for Hungary. The value set enables to evaluate the cost utility of health technologies for children and adolescents based on societal preferences in Hungary.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40273-022-01190-2.

Effects of resource availability on the web structure of female western black widows: is the web structure constrained by physiological trade-offs?

AbstractA major challenge of biological research is to understand what generates and maintains consistent behavioral variation among animals. Time and energy trade-offs, where expressing one behavior is achieved at the expense of another, are often suggested to favor the maintenance of behavioral differences between individuals. However, few studies have investigated how individuals adjust their allocation to different functions over time and depending on resource abundance. Black widow spiders of the genus Latrodectus build persistent webs that include structural threads which protect against predators and sticky trap threads to capture prey. Web structure consistently differs among individuals in the number of trap and structural threads. To quantify the intensity of a trade-off, we assessed the relationship between the number of structural and trap threads and tested whether varying food abundance affected individual differences in web structure. We further quantified how these individual differences change over time and with food abundance. We subjected spiders to three different levels of prey abundance and monitored the structure of their webs every twelve hours. We found no evidence for a trade-off between trap and structural threads. Instead, spiders that produced more structural threads also produced more trap threads, showing that spiders invested equally in both types of threads. Interestingly, the magnitude of individual differences in web structure was greatest when spiders were fed ad libitum and at the beginning of web construction. We suggest that variation in web structure between spiders could be the result of stable developmental differences in morphology or genetic differences.